Internet Explorer java version

i have java 1.4.08 installed on my windows machine.
a particular application requires Java 1.5 as the java version for the internet explorer . all my current applications use java 1.4.08. if i install 1.5.03, will it cause any problem for the existing applications?
Also when i set the java version for the browser through the control panel, all subsequent IE windows will have java 1.5 . is there any method through which i can launch an instance of IE with a particular version of java?